ECR plasma CVD (chemical vapor deposition) which forms a deposit film on a substrate by utilizing the ECR plasma reaction has an advantage such that it allows a low-temperature formation of the film and gives a less damage to the substrate. Further, the ECR plasma etching has some features that the exposure damage is small, the etching selection ratio is high and the anisotropic etching is possible, and forms one of the important etching methods in carrying out a highly fine processing on the substrate.
As the apparatus for etching or formation of a deposit film by utilizing the ECR, two typical examples have conventionally been known. FIG. 1 illustrates a first example, and FIG. 2 illustrates a second example. According to the apparatus of FIG. 1, a TE.sub.11 mode microwave 8 is introduced into a plasma formation chamber 1 from a magnetron 6 through a waveguide 5, and an ECR area 9 is formed by the interaction between the microwave 8 and the magnetic field generated by a coil 3. A reactive gas plasma formed by this ECR is conveyed through a plasma stream into the etching chamber 2 by the divergent magnetic field caused by the coil 3, where a substrate 14 is etched by ion impact. (See Japanese Patent Laid-Open No. 56-155535.)
According to the apparatus of FIG. 2, within the plasma formation chamber 1, the substrate 14 is disposed remote from the ECR area 9 by a predetermined distance. In this arrangement, a local separation of electrons and ions takes place within the reactive gas plasma prevailing within the plasma formation chamber 1, and a resulting static electric field causes the ions to be withdrawn from the gas and to be exposed onto the substrate 14 for process such as formation of the deposit film or the like. (See Japanese Patent Laid-Open No. 60-134423.)
Each of the two apparatus is designed to form the ECR area 9 within 5 cms (centimeters) from the microwave introducing window of the plasma formation chamber 1. Further, since there exists the electric field intensity distribution of the TE.sub.11 mode microwave 8 in the waveguide 5 as shown in FIG. 3, an unevenness takes place in the density distribution of the plasma generated in the chamber 1. In order to avoid the undesired effect of the uneven density distribution of the plasma, the substrate 14 is disposed at a sufficient distance from the ECR area 9.
Further, as shown in FIG. 4, the center frequency of the microwave 8 equals 2.45 GHz, and its frequency bandwidth is in the range of 2.45 GHz +-1 MHz. Further, the magnetic field applied to the microwave 8 by the coil 3 has a gradient of the flux density as shown in FIG. 5. In the apparatus of FIG. 2, the magnetic field gradient equals about 40 Gauss/cm in the ECR area 9 which is formed 2 cms above the substrate 14.
However, in the two apparatus, in order to obtain an uniform plasma density distribution on the substrate 14, the substrate 14 is disposed at a sufficient distance from the ECR area 9. As a result, the plasma density becomes low, and practical speeds of process such as the film deposition and the etching cannot be obtained.
Further, since the bandwidth of the introduced microwave is very narrow such as +-1 MHz, the microwave absorbing efficiency is low, and a high density plasma cannot be obtained. In consequence, the ion current becomes low, and the practical processing speeds cannot be achieved.
Accordingly, an object of the present invention is to provide a method of generating a higher density plasma so that the processing speed of the substrate is improved by increasing the ion current.
Another object of the present invention is to provide a method of achieving the uniform density distribution of the plasma generated at the ECR area to allow the substrate processing such as etching or deposit film formation in the vicinity of the ECR area.